At the present time, terrorism constitutes a great threat to international and domestic social stability. Governments of countries are endeavoring in anti-terrorism. Detection technology of contraband such as explosives is the core of anti-terrorism.
An existing contraband detection technology is x-ray imaging detection technology. X-ray imaging detection technology is a broadly applied safety inspection technology. Many devices based on the x-ray imaging detection technology can be seen in airports and at railway stations. Since x-ray mainly reacts with the orbital electrons outside the atomic nucleus, it has no capability in distinguishing the characteristics of the atomic nucleus. Therefore, only the density (mass thickness) of the detected object can be measured using x-ray, and it is impossible to determine the kinds of elements of the detected object. In practice, when contraband is mixed with daily articles and the density thereof is hard to be distinguished from that of the daily articles, it is difficult to find the contraband by the x-ray imaging detection technology. Although some new x-ray imaging detection technologies, for example, dual-energy x-ray and CT technology, have been somewhat improved in recognition or discrimination capability, they still cannot overcome the inherent disadvantage of inability to recognize the kinds of elements.
Another existing illicit-article detection technology is neutron type detection technology. As to the neutron type detection technology, neutrons can react with the atomic nucleus of a substance and emit characteristic γ-rays. It is possible to determine the kinds of the elements of the analyzed substance based on the energy spectrum of γ-rays. A disadvantage of the neutron type detection technology is modest imaging resolution which, at best, reaches a spatial resolution of 5 cm×5 cm×5 cm at the present time, far lower than the millimeter-grade resolution of x-ray imaging. Additionally, a separate neutron source is usually expensive and limited in life-time, and neutron yield is not high enough.
Therefore, a method and/or system is desirable which is capable of combining the above-mentioned x-ray imaging detection technology and neutron type detection technology so as to obtain the advantages of high resolution of the x-ray imaging detection technology and the element recognition capability of the neutron type detection technology.
U.S. Pat. No. 5,078,952 refers to an explosive detection system which combines a plurality of detecting means including an x-ray imaging means and a neutron detecting means to realize high detection probability and lower false positive. U.S. Pat. No. 5,078,952 further discloses associating the data obtained by the x-ray imaging means with the data obtained by the neutron detecting means so as to make up, with a high resolution x-ray image, for the of the low resolution of the neutron type detection technology. However, an x-ray source and a neutron source, which are independent of one another, are used in U.S. Pat. No. 5,078,952, and so the cost thereof is more expensive.
A neutron generating technology can be used to bombard a conversion target with x-rays to generate neutrons from the conversion target. The neutrons generated in this way can be called photoneutrons. This photoneutron generating technology provides a possibility of generating both x-rays and neutrons from single source, which would reduce cost as compared to generating x-rays and neutrons using two sources respectively.
International Patent Application Publication WO 98/55851 refers to a system of detecting and recognizing contraband by photoneutron imaging and x-ray imaging. The system works in two steps. Specifically, the system first generates an x-ray beam using a linear accelerator x-ray source and detects an object by x-ray imaging. If no abnormality is found, the detected object is allowed to pass; if a suspect region is found, a photoneutron conversion target (beryllium) is temporarily inserted into the x-ray beam so as to generate photoneutrons, and the suspect region is detected based on characteristic γ-rays emitted from the radiative capture reaction between the photoneutrons and the atomic nucleus of the substance. The system performs the first step of detection using only x-rays. Due to the limit of the recognition capability of the x-ray imaging detection technology as stated above, the system has a low probability of detection (PD). Besides, the system does not simultaneously generate x-rays and photoneutrons for detection, but generates x-rays and photoneutrons for detection in two separate steps. That is, only x-rays and no photoneutrons are generated in one step, while photoneutrons are generated using the x-rays in another step. However, the x-rays generated in said another step are only used for generation of photoneutrons not for detection purpose. Further, the generated photoneutrons are only used for detection of the suspect region of the detected object; not for overall detection of the detected object.
Chinese Patent Application No. 200510086764.8 discloses a method of recognizing materials using fast neutrons and x-rays. The application describes a method and device of simultaneously generating x-rays and photoneutrons, which splits the x-rays generated by an accelerator into two beams one of which is used in generating photoneutrons. In the application, however, as far as the neutrons are concerned, detection is performed by way of the intensity of photoneutrons that pass through the object to be detected; not by way of the characteristic γ-rays emitted from the reaction between the neutrons and the detected object. Additionally, such a detection usually requires for the x-ray beam to be laterally spaced apart from the neuron beam by a distance in order that the x-ray beam and the neutron beam do not interfere with one another in their detections.
The contents of each of the above-referenced applications and patents are hereby incorporated by reference in their entireties.